Burner for solid fuel

ABSTRACT

The invention relates to a burner for solid fuel containing a space for a solid fuel to be burned, in which solid fuel space the flow of gas is arranged to be possible. The burner comprises at least one fire pipe ( 3,13 ) inside the solid fuel space, through the wall of which a possibility for gas flow is arranged.

[0001] The present invention relates to a burner for solid fuelcontaining a space for solid fuel to be burned, in which solid fuelspace flow of gas is arranged to be possible.

[0002] Solid fuel burners are disclosed in the following publications:

[0003] Publication GB 2101737 discloses a grate to be placed in afurnace, said grate comprising low side walls. The grate can be moved inthe furnace in such a manner that for example the cleaning of thefurnace is facilitated.

[0004] Publication U.S. Pat. No. 2,949,209 discloses a waste burnerwhose walls contain holes for air intake.

[0005] Publication U.S. Pat. No. 3,213,846 discloses a furnace that canbe used both for heating and cooking.

[0006] Publication U.S. Pat. No. 4,719,899 discloses an arrangement forefficient burning of granular fuel.

[0007] Publications U.S. Pat. No. 5,941,234 and WO 98/29686 disclose aburner equipped with holes for air intake, the bottom of which burner isadvantageously in an oblique position. The burner can be used infurnaces, such as ovens and fireplaces.

[0008] Publication U.S. Pat. No. 5,983,885 discloses a furnace in whichpellets can be constantly supplied.

[0009] Solid fuel burners can be separate burners placed inside afurnace, burners used without a surrounding furnace, or the burner canbe furnace with a mantle that stores thermal energy. Known furnacescomprising a heat storing mantle are typically fireplaces or ovens orcombinations of these. The mantle can be for example made of tiles orsteatite.

[0010] In known burners of solid fuel the fuel charge is usually litfrom outside and the combustion is directed from outside the fuel chargeto the inside. The fire propagates towards the centre of the fuel chargefrom all sides, wherein combustion takes place slowly and in anuncontrolled and imperfect manner. The combustion causes a great deal ofsmoke and the burning temperature is low, wherein large amounts ofunburned gases are produced. Substantial production of smoke causesstains the air conduits and the efficiency of the combustion is poor.

[0011] By means of the burner according to the invention it is possibleto avoid the above-mentioned problems. The solid fuel burner accordingto the invention is characterized in that it comprises at least one firepipe inside the space for solid fuel, a possibility for gas flow beingarranged through the wall of said fire pipe.

[0012] In the burner according to the invention, solid fuel such as woodchips, pellets, sawdust, peat or chopped wood burns in a controlledmanner almost completely and the combustion gases produced during thecombustion are so pure that they do not stain the air conduits. Thecombustion takes place substantially at constant efficiency. Pelletsthat contain a great deal of energy in relation to their volumeconstitute especially advantageous solid fuel.

[0013] In order to be able to safely use the burner with a goodefficiency and in such a manner that the burner is durable in use, thefire pipe must extend above the level determining the upper level of thesolid fuel space. In other cases the efficiency of the burner must berestricted unnecessarily, because there is a risk that the burner isdamaged as a result of excessive heat. In addition to theabove-mentioned advantages it is also possible to attain a simplestructure by means of such an arrangement, because additional parts fordirecting the fire are not necessary. In practice, the level determiningthe upper surface of the solid fuel space is often the point where thecover closing the solid fuel space is placed.

[0014] According to an embodiment of the invention, the solid fuelburner according to the invention can be placed in an existing furnace,such as an oven, a fireplace or a stove. One preferred target of use isa heat storing fireplace equipped with doors. According to a secondembodiment of the invention the burner can be without the surroundingfurnace as such. According to a third embodiment of the invention theburner is a furnace comprising a heat storing mantle, a dischargeopening for combustion gases and a combustion space. During thecombustion heat energy binds itself to the heat storing mantle of thefurnace, which can be made of for example tiles or steatite.

[0015] The size of the burner varies according to the use. Solid fuelcan be supplied in the burner in one fuel charge or the burner can befilled up constantly as the combustion continues. Typically, however,the burner is filled before fire is set therein, and thereafter the fuellocated in the burner is burned without adding new fuel. The burner canbe used for example for heating of one-family houses or water. In theburner according to the invention the burning takes place in such amanner that the solid fuel is gasified and the gasified fuel burns inthe middle of the burner.

[0016] The burner according to the first and second embodiment of theinvention comprises at least a container and a fire pipe. Furthermore,it can also contain a cover, an air intake pipe and a grate. Thecontainer comprises at least one side wall and a base. The number of theside walls depends on the shape of the container. Advantageously, thecontainer has a cylindrical shape, wherein there is only one side wall.The container can be placed vertically or horizontally. The containerhas a space for solid fuel a possibility for gas flow is arranged withinthis space. The side walls of the container can have air intake openingsspread evenly over the entire surface area of the side walls. The shapeof the air intake openings can be selected freely according to thedesired outer appearance. However, the location of the air intakeopenings is significant for guiding radiating heat to a desired target.The solid fuel space can also be another container to be placed insidethe container, the wall of which is for example net-like, wherein theflow of gas is possible via the space remaining between the walls of thecontainers.

[0017] In the container, advantageously in its side wall, there is alead-through advantageously for a cylindrical air intake pipe. The airintake pipe is installed to a substantially horizontal position via thelead-through. The diameter of the air intake pipe is selected accordingto the use. The air intake pipe is connected to a fire pipe installed ina substantially vertical position inside the container.

[0018] The fire pipe has advantageously a cylindrical shape and apossibility for gas flow is arranged through the wall of the same. Thepossibility for gas flow can be arranged in such a manner that the wallof the fire pipe contains openings in such a manner that at least 30% ofthe surface area that is located inside the container consists of theopenings. The fire pipe can be supported from its upper part with acover that is placed on top of the container and contains a lead-throughfor the fire pipe. The cover is not, however, necessary in the burner,but the burner can also be used without the cover. The fire pipe isadvantageously located in the container in such a manner that it ispositioned vertically in the middle of the container. When the containerhas a large volume and the amount of solid fuel is large, it is possibleto use several fire pipes at fixed intervals.

[0019] In the lower part of the fire pipe, above the air intake pipethere is a grate containing a lead-through for the fire pipe. The grateis advantageously a perforated plate extending to the walls of thecontainer, or a suitably rigid net that is similar in shape with thecross-section of the container.

[0020] The burner is composed of high temperature and fire resistantmaterials, advantageously of metal. The raw materials of the burner canvary depending on the number of times of use the burner is desired to beusable, as well as how large container volumes are utilized. Thedimensioning of the burner is conducted on the basis of optimalcombustion conditions. If the gas remains too poor, combustion does nottake place. One important factor is the distance of the fire pipe fromthe wall of the container, in other words the layer of fuel that remainsbetween the fire pipe and the inner wall of the container.

[0021] The burner according to a third embodiment of the invention,which is a furnace, comprises a heat storing mantle, a discharge openingfor combustion gases and a combustion space. The combustion space isrestricted by the heat storing mantle of the furnace and the mouth ofthe furnace, which can contain doors that can be closed. The combustionspace comprises a fire pipe, through the wall of which a possibility forgas flow is arranged. The fire pipe is a pipe installed inside thefurnace in a substantially vertical position, said pipe tapering offtowards its upper end. The cylindrical mantle of the pipe containsopenings whose total surface area is at least 30%, advantageously atleast 40%, of the entire surface area of the mantle wall of the firepipe. The openings of the fire pipe travel advantageously diagonally onthe wall of the mantle of the fire pipe, so that when their traveldirection is examined from outside to the inside, the travel directionis upwards from a lower level. It is a purpose of this arrangement tokeep the openings of the fire pipe open, in other words ash does notaccumulate on the wall of the fire pipe, but it flows out of theopenings. It is important that the openings are oblique, because thematerial of the wall of the fire pipe is relatively thick. The wall ofthe fire pipe is made of fireproof material, for example of ceramics oriron alloy. The fire pipe is advantageously made by casting.

[0022] Between the wall of the furnace and the fire pipe there is apartition wall equipped with air intake openings. It is a purpose of thepartition wall to form inside itself but outside the fire pipe a fuelspace in which the fuel is located. When seen from outside to theinside, the travel direction of the air intake openings isadvantageously upwards from a lower level. The partition wall can be acontinuous wall that has a shape of a cut cone or cylinder, or it can beformed of several parts connected to each other.

[0023] Outside the mantle of the fire pipe, in the upper part of thefire pipe there is a cover that closes the combustion space and assistsin directing the combustion to the fire pipe and for its part promotesthe reduction of discharge. The cover is usually located on the samelevel with the lowest part of the doors of the furnace, and the firepipe extends at least slightly over the level of the cover.

[0024] Below the combustion space of the furnace there is an ash space.The combustion space and the ash space are separated by an adjustablegrate that can be formed of two superimposed fire grates. The grate canbe adjusted manually or automatically.

[0025] Fire can be set into the furnace with an automatic function forexample in such a manner that in the vicinity of the fire pipe there isan electric resistance that sets the fuel on fire at a predeterminedmoment of time.

[0026] The act of closing and opening the discharge opening of thecombustion gases as well as the adjustment of the holes of the grate canalso be arranged by means of an automatic function. The automaticfunctions are preferably connected to each other to occur in a setorder, and measurement functions may be connected thereto to determinethe moment of a certain event.

[0027] In the following, the invention will be described with referenceto the appended drawings, in which

[0028]FIG. 1 shows a cross section of the solid fuel burner according tothe first and second embodiment of the invention, and

[0029]FIG. 2 shows a cross section of a furnace according to the thirdembodiment of the invention,

[0030] The solid fuel burner according to FIG. 1 comprises a container 1that is composed of a cylindrical wall and a round base element. Thecylindrical section is equipped with air intake openings 6 spread atequal intervals on the entire surface area of the cylinder. Thecontainer may contain handholds or handles by means of which it ispossible to carry the burner. The lower part of the vertical wall of thecontainer 1 contains a lead-through for an air intake pipe 2 to beinstalled in a substantially horizontal position. The diameter of theair intake pipe is selected according to the use, in a 20-litrecontainer it may be 50 mm. Advantageously, the air intake pipe has acylindrical shape.

[0031] The air intake pipe 2 is connected to a fire pipe 3 placed in asubstantially vertical position, said fire pipe containing alead-through for the air intake pipe 2. The lead-through can be forexample an area removed from the lower part of the fire pipe 3, in whichit is possible to fit the end of the air intake pipe 2. Advantageously,the fire pipe 3 has a cylindrical shape and it is perforated in such amanner that it contains openings 7 with a diameter of approximately 5mm, the total surface are of which is over 30% of the entire surfacearea of the fire pipe. The openings are spread evenly at least over theentire surface area of the wall of the fire pipe that remains inside thecontainer 1. In a 20-litre container the diameter of the fire pipe canbe 100 mm. The fire pipe is advantageously installed in such a mannerthat it is in a vertical position inside the container 1, wherein theperpendicular distance of the fire pipe 3 to the wall of the container 1is equally large everywhere. The fire pipe 3 can be supported forexample with three horizontal iron bars placed in a suitable location inthe height direction of the container, said iron bars pointing atdifferent directions and being attached to the inner wall of thecontainer 1 and touching the outer surface of the fire pipe 3. The firepipe 3 extends above the level determined by the cover 4.

[0032] The cover 4 is intended to be placed on top of the container 1during burning, said cover containing a lead-through for the fire pipe3. The cover 4 is not essential, but it is necessary so that smokingcombustion does not occur on the surface of the fuel layer and when theburner is moved, ash is not spread out of the burner.

[0033] The air intake pipe 2 supports a grate 5 that is a perforatedround plate or a rigid net. The diameter of the holes is over 5 mm. Inthe middle of the grate 5 there is a lead-through for the fire pipe 3.The grate 5 promotes the combustion in such a manner that the fire diesdown rapidly and it is possible to close the damper of the furnaceearlier than in a situation where the burner is used without the grate5.

[0034] The burner is used in such a manner that the container 1 isadvantageously filled up to the brim in the volume above the grate 5with solid fuel, such as pellets, wood chips or sawdust. The fire pipe 3is advantageously surrounded with solid fuel advantageously in such amanner that the fire pipe 3 is in the middle of the burner. The cover 4is positioned in its place after the filling. The burner is transferredto the furnace, in which the cross section of the air conduit should belarger than the cross section of the fire pipe, and kindling is placedon the bottom of the fire pipe 3, said kindling being for exampletightly bundled paper that has been moistened with a suitable lighterfluid, for example with the lighter fluid for barbecue coal.Approximately 50 grams of kindling is a suitable amount. Fire is set inthe burner setting the kindling on the bottom of the fire pipe 3 on firevia the air intake pipe 2.

[0035] The lighting phase takes a few minutes. At the lighting stageheat rises in the fire pipe 3 and gas starts being distilled from thefuel. The suction of the fire pipe 3 draws air through the wall of thecontainer 1 via openings 6, and at the same time the distilled gasstarts to flow from the edges of the container to the middle and furtherthrough the wall of the fire pipe 3 via openings 7, and the combustionof the gas begins. The burner burns with free draught, in other wordsair travels freely in the burner. The gas burns in a strong flame in thefire pipe 3 until the fuel ends. The duration of the burning depends forexample on the moisture content of the fuel. When naturally humid woodchips are used in a 20 litre container with a air intake pipe 2 whosediameter is 50 mm, and a fire pipe 3 having a diameter of 100 mm, thelighting stage typically takes 5 to 10 minutes, and the actualcombustion 20 to 90 minutes. The result is ash which is chilled in theburner inside the furnace before it is removed from the burner.

[0036] During the combustion high temperatures are produced when gascontaining carbon monoxide burns in the fire pipe 3. The pillar ofburning gas can extend 200 to 700 mm over the fire pipe. If for somereason one wishes to interrupt the burning, the end of the air intakepipe 2 is closed and time is allowed to pass until the flames arelowered in the upper end of the fire pipe 3. Thereafter the upper end ofthe fire pipe 3 is closed, and the burner is wrapped in a fire-blanketor the like to be transferred out for final extinguishing.

[0037]FIG. 2 shows a cross section of a furnace according to theinvention. The mass of the furnace is advantageously 800 to 1000 kg, theenergy output of the same is 8 to 10 kW/h at the highest. The amount offuel burned at a time that advantageously consists of pellets, is 8 to10 kg at the highest. The travel directions of the gas flows are shownby means of arrows in the drawing.

[0038] The furnace comprises a heat storing mantle 8, an adjustableopening for combustion gases (not shown in the drawing) and a combustionspace 9. Replacement air flows to the air space 11 of the combustionspace 9 via the air intake openings 10 located in the mantle 8.

[0039] In the middle of the combustion space 9 there is a fire pipe 13,outside and around of which pellets have been placed in the fuel space12. On the wall of the fire pipe 13 there are openings 16 for flow ofair. The diameter of the openings is advantageously 10 mm, and theycover approximately 40% of the surface area of the wall of the fire pipe13. The openings of the fire pipe 16 extend from outside the fire pipeto the inside, when seen upwards from a lower level. The fire pipe 13 isopen both in its upper and lower end. The cylindrical shape of the firepipe 13 and on the other hand its mass guarantee that the fire piperemains stationary. The conical shape together with the controlled flowof air promotes the combustion process, in other words the time it takesfor the fire to die down is reduced. The material of the fire pipe canbe ceramics, and the advantageous wall thickness is 8 to 12 mm. Anotheralternative for the material of the fire pipe is a fireproof iron alloy,wherein it is possible to utilize thinner walls than in connection withceramics. The fire pipe 13 extends above the level determined by thecover 17.

[0040] The fuel space 12 is restricted from the air space 11 by apartition wall 14 that is equipped with openings 15 that enable the flowof replacement air. When seen from outside to the inside, the traveldirection of the openings is downwards from an upper level, and theopenings 15 are advantageously in an angle of 20° with respect to thevertical direction. Thus, the burning mass of fuel does not escapeoutside the fuel space 12. The partition wall 14 can be an element withthe shape of a cut cone that expands towards its upper part.Alternatively, the partition wall can have a cylindrical shape, whereinthe mantle of the furnace 8 must be shaped in such a manner that the airspace 11 can be formed or the diameter of the cylinder must besubstantially smaller than the combustion space. The partition wall canbe made of ceramics, and an advantageous thickness of the partition wallis thus approximately 25 mm. The partition wall can also be made offireproof iron alloy.

[0041] In the upper end of the fire pipe 13, around the same in asubstantially horizontal position is a cover 17 closing the combustionspace, said cover controlling the burning so that it takes place in thefire pipe 13 The upper surface of the cover 17 is typically on the samelevel with the lowest part of the doors of the furnace at the highest(not shown in the drawing) in such a manner that the fuel space 12 canbe filled through the doors. The cover 17 promotes the completecombustion of the fuel and thus affects the amount of discharge. Thecover 17 is preferably releasable, it can be formed of several parts,and it can be for example pivoted in the mantle 8, and/or the parts ofthe cover can be pivoted to each other.

[0042] The fire pipe 13 is erected on top of the grate that is composedof two fire grates 18 a and 18 b. The fire grate 18 a is stationary andthe fire grate 18 b is movable. The stationary fire grate 18 aadvantageously contains holes with a diameter of 16 m, and they cover 30to 50% of the surface area that remains inside the partition wall 14.The stationary fire grate 18 a can extend to the side of the air space11 in such a manner that it forms a plane on top of which the partitionwall 14 can be installed. Both fire grates are perforated in such amanner that air can travel through the grate. The perforation isarranged in such a manner that by moving the fire grate 18 b theopenings in the sections of the grate located underneath the fire pipebecome larger during the combustion and the openings in the section ofthe grate around the fire pipe become smaller. By means of thisarrangement the aim is to ensure that the combustion air is sufficientin the fire pipe 13. In a preferred embodiment the holes have a maximumdiameter of 16 mm, and minimum diameter of 6 to 8 mm. By moving the firegrate 18 b when there is no fire in the furnace, it is possible to makethe holes in the section of the grate remaining outside the fire pipe 13larger and thus ash can be removed from the grate. In the area of theair space 11 in the fire grate there are not necessarily any holes.

[0043] Below the grate there is an ash space 19 which can be a box thatcan be taken out of the furnace to be emptied. In the mantle of thefurnace there may be a door or the like for removal of the box, or itcan be removed via the cover 17. The height of the ash space isadvantageously approximately 15 cm.

[0044] To be able to fill the ash space, it is possible to use forexample a can similar to a watering can which contains an oval base andflexible elongated pouring tip with a sufficiently large diameter. Thecover 17 that closes the combustion space is opened for the duration ofthe filling and pellets are poured in the fuel space 12 by tilting thecan. Another possibility is to use filling automatics that can conductthe filling in one or several stages, possibly also continuously duringthe combustion.

[0045] Fire is advantageously set into the furnace outside the fire pipe13 by means of an electric resistance of 300 to 500 W that is installedinside the fuel space 12, the operating time of which resistance and thestarting moment of the lighting can be controlled with an automaticfunction. The grate and the smoke damper of the furnace can be adjustedwith an automatic function, such as by means of amicroprocessor-controlled servomotor. The control of the electricresistance, the grate and the smoke damper of the furnace can bearranged as successive operations, wherein before the fire is set, thegrate and the smoke damper are adjusted in a position suitable for thecombustion. After the fire is set, the smoke damper is prevented frombeing closed for a period of time assumed as a combustion time. However,the smoke damper is closed only after the system receives informationfor example from a combustion gas detector that the concentration of thecombustion gas has been reduced on a level that allows the closing ofthe damper.

[0046] Furthermore, the furnace may contain a unit intended for cleaningof combustion gases, which unit can be located in a suitable point inthe exit route of combustion gases. The purpose of the cleaning unit isto remove all the small residues that possibly remain in the combustiongas when it exits to the outside air.

[0047] The invention is not restricted to the description above, but itmay vary within the scope of the claims. In the solutions according tothe first and second embodiment of the invention for example thefollowing changes are possible: The solid fuel can also be waste, if thegasification of the same is sufficient for maintaining combustion. Theair intake pipe and the fire pipe may be connected into one pipe. Thepart closing and opening the container is not necessarily the coverlocated on top of the container, but it can be some other part. Thecontainer may be equipped with legs, wherein in the bottom of the samethere may be air intake openings, wherein the grate and/or air intakepipe is not absolutely necessary. Generally it can be said that theinvention can be modified according to the environment in which it isused. In the solutions according to the third embodiment of theinvention for example the following changes are possible: Thegeometrical shapes, sizes and placement of the different parts of thefurnace with respect to each other may differ from that presented above.It is possible that the furnace has several fire pipes, which can beconnected by intermediate air channels. The intermediate air channelsmay comprise conical pipes with closed ends that are installed in avertical position, as well as pipes connecting the same.

1. A solid fuel burner containing a space for solid fuel to be burned,the space being bordered by a base, a top and at least one side wall,and inside the space there is at least one substantially vertical firepipe (3, 13) provided with openings (7, 16) in its wall and open fromits both ends, characterized in that the at least one side wall of thespace is equipped with air intake openings (6, 15) between the base andthe top provided with a cover (4, 17), and the fire pipe (3, 13) isarranged to extend through the cover (4, 17).
 2. The burner according toclaim 1, characterized in that the fire pipe (3, 13) is a perforatedpipe arranged in a substantially vertical position in the solid fuelspace, in which pipe the surface area of the openings (7, 16) is over30%, advantageously at least 40% of the entire surface area of the wallof the fire pipe remaining inside the solid fuel space.
 3. The burneraccording to claim 1 or 2, characterized in that it is arranged todistil combustible gases from solid fuel and to burn them in the firepipe (3, 13).
 4. The burner according to any of the preceding claims,characterized in that it is arranged to burn pellets.
 5. The burneraccording to claim 1, characterized in that it is a burner that can bepositioned in an existing furnace, or it can be used as such without thesurrounding furnace.
 6. The burner according to claim 5, characterizedin that the solid fuel space is a container (1).
 7. The burner accordingto claim 5 or 6, characterized in that the burner comprises an airintake pipe (2) installed in a substantially horizontal position, saidair intake pipe (2) being connected to the lower part of the fire pipe(3) inside the container (1).
 8. The burner according to any of thepreceding claims 5 to 7, characterized in that it comprises a grate (5)within a fixed distance from the bottom of the container (1), inside thesame.
 9. The burner according to any of the preceding claims 5 to 8,characterized in that it has free draught.
 10. The burner according toclaim 1, characterized in that it is a furnace comprising a heat storingmantle (8), a discharge gate for combustion gases and a combustion space(9) comprising a fuel space (12) forming the solid fuel space.
 11. Theburner according to claim 10, characterized in that the fire pipe (13)is a pipe with a cut conical shape, tapering towards its upper end, thatis equipped with openings (16).
 12. The burner according to claim 11,characterized in that the openings (16) of the fire pipe (13) extend inthe wall of the fire pipe from outside to the inside and upwards from alower level.
 13. The burner according to any of the preceding claims 10to 12, characterized in that the fire pipe (13) is made of fireproofmaterial, such as ceramics or iron alloy.
 14. The burner according toany of the preceding claims 10 to 13, characterized in that underneaththe combustion space there is an ash space (19).
 15. The burneraccording to claim 14, characterized in that between the ash space (19)and the combustion space (9) there is an adjustable grate.
 16. Theburner according to claim 15, characterized in that the grate isarranged adjustable by means of an automatic function.
 17. The burneraccording to any of the preceding claims 10 to 16, characterized in thatbetween the mantle (8) and the combustion space (9) there is a partitionwall (14) equipped with air intake openings (15).
 18. The burneraccording to any of the preceding claims 10 to 17, characterized in thatthe furnace is arranged to be lit by means of an automatic function. 19.The burner according to any of the preceding claims 10 to 18,characterized in that the closing and opening of the discharge openingof the furnace is arranged by means of an automatic function.